In the microelectronics industry as well as in other industries involving construction of microscopic structures (e.g. micromachines, magnetoresistive heads, etc.), there is a continued desire to reduce the size of structural features. In the microelectronics industry, the desire is to reduce the size of microelectronic devices and/or to provide greater amount of circuitry for a given chip size.
The ability to produce smaller devices is limited by the ability of lithographic techniques to reliably resolve smaller features and spacings. The nature of optics is such that the ability to obtain finer resolution is limited in part by the wavelength of light (or other radiation) used to create the lithographic pattern. Thus, there has been a continual trend toward use of shorter light wavelengths for lithographic processes. Recently, the lithography using 193 nm imaging radiation has become more widespread for producing small features.
A resist composition must possess desirable optical properties to enable image resolution at a desired radiation wavelength as well as suitable chemical and mechanical properties to enable transfer to the image from the patterned resist to an underlying substrate layer(s). Thus, a patternwise exposed positive resist must be capable of appropriate dissolution response (i.e. selective dissolution of exposed areas) to yield the desired resist structure. Given the extensive experience in the lithographic arts with the use of aqueous alkaline developers, it is important to achieve appropriate dissolution behavior in such commonly used developer solutions. The patterned resist structure (after development) must be sufficiently resistant to enable transfer of the pattern to the underlying layer(s). Typically, pattern transfer is performed by some form of wet chemical etching or ion etching.
In the past, it was thought that 193 nm lithography would be succeeded by 157 nm lithography in order to reach the 45 nm critical dimension node. Recently, however, the lithography roadmap has been altered by the proposed use of 193 nm immersion lithography which promises to extend 193 nm lithography to the 45 nm node and perhaps beyond.
While some resist compositions have been designed for use in conventional 193 nm lithography, there is a need for improved resists that are capable of imaging features at critical dimensions of 50 nm or less across large (300 mm) wafers. Acrylate/methacrylate resists have been the most widely accepted for use with 193 nm radiation, however these resists generally do not provide adequate critical dimension control across a wafer at critical dimensions below 65 nm. Thus, there is a need for improved acrylate/methacrylate resist compositions useful at the reduced dimensions promised by 193 nm immersion lithography. One contributing factor to lack of critical dimension has been post-exposure bake sensitivity. Thus, there is a desire for acrylate/methacrylate resists with reduced post-exposure bake sensitivity and/or acrylate/methacrylate resists which can be processed without post-exposure bake.